The invention relates to an automatic depth compensation system which holds the depth of a sleeve bore on a workpiece. Originally, adjustments of the tool were made manually. That is, the bore and length of the workpiece would be measured with a gauge means, and any adjustments were made manually. Later developments provided for automatic movement of the tool to provide for compensation of the bore diameter, such as disclosed in U.S. Pat. Nos. 3,620,131 and 3,620,132. U.S. Pat. No. 3,995,528 discloses a tool length compensation which programs the performance of each tool used. U.S. Pat. Nos. 3,965,621 and 4,195,250 disclose automatic measuring and tool position compensating systems. U.S. Pat. No. 3,950,427 discloses a zero offset for machine tool control.
The present invention includes means responsive to a depth compensation signal indicated by gauge means located in a following station. The signal controls a power supply to a stepping motor located at the rear of a spindle. The motor is selectively energized to turn an inner, threaded sleeve in a tool body which effectively changes the relationship of a tool point relative to register spots on a workpiece. One unique feature comprises a "bootstrapping" effect wherein the shaft that turns the threaded sleeve to position an axially movable stop ring also serves as a torque arm to prevent the ring from rotating. A further feature is that the movable stop is the adjustable member in the system rather than the tool point itself.